New Poll: Moon Yes, Mars No

[spacester]

<font color="yellow">So you are saying that it is not possible to hit Mars anywhere in its orbit from anywhere in Earth's orbit given enough time and propellant? I'm not saying this is a good idea, just that it is possible.</font><br /><br />A well phrased question, thank you. Certainly, from everything I’ve learned, my initial response is an emphatic “yes, that is what I’m saying . . . it’s not just time (time of flight) and deltaV, it’s also <i>timing.</i> If you don’t time it right, you fail. But more than that, there is a range of Earth-Sun-Mars angles from which you cannot go from here to there.”<br /><br />(I need to do this in three posts . . .)<br /> <div class="Discussion_UserSignature"> </div>

 

[spacester]

To digress a bit, I have to say that the reason I took up the study of interplanetary orbital mechanics in the first place was because it seemed to me that the experts were too negative. It seemed like all they would talk about is what is impossible. I did not dispute such, but I felt that no one was talking about what was possible. (Except Buzz, of course)<br /><br />Sometimes, I think folks forget the basic fact that no matter what, you are in orbit around the Sun. All interplanetary trajectories are just an elliptical arc - a portion of the ellipse of your orbit. One focus of this orbit is the Sun. The start point of this arc is the Earth at time of insertion into this heliocentric orbit. This constrains you quite a bit in what you can actually do without Star Trek type capability. You need to do things just right to get the end of the arc to intersect Mars’ orbit at the same time it happens to be there.<br /><br />As I used the web to learn how it was done, at first all I could find was Hohmann’s solution; finally I found an excellent source on one-tangent transfers. Much digging later and I found Lambert’s solution. These are all the different transfer orbits AFAIK. The only other way to do it is with a hyperbolic orbit. That’s hyperbolic relative to the sun – you’re going so fast you will leave the solar system if you don’t apply massive amounts of braking energy.<br /><br />Those four methods are ranked in increasing order of energy, and there is a (complicated) inverse relationship between energy and time of flight. These four flight paths are not that hard to conceive. (Put “opposition class” and “conjunction class” aside for a bit, they do not lead to a general understanding of what’s going on.)<br /><br />Hohmann is minimum energy because you spend just enough energy to get to Mars orbit and no more, while leaving Earth on a tangential trajectory. To get there in less trip time, you spend some energy to (*edit*) tweak your semi-latus rectum a tiny bit, modifying <div class="Discussion_UserSignature"> </div>

 

[spacester]

OK, so that was the background. Back to the question at hand.<br /><br />Given:<br />You’ll be leaving Earth or Earth orbit and your destination is Mars<br />No gravity assists.<br />No continuous thrust (no ion engines)<br /><br />Q: Is it possible to leave any time you want, and by using whatever time of flight and whatever energy you need to make it work, rendezvous with Mars?<br /><br />When my program seeks a solution, it finds the Earth-Sun-Moon angle (“phase angle” or “lead angle”) needed to set the time of launch. These range from 32.16 degrees for outbound Hohmann to 33.32 for 200 day one-tangent to 28.63 for 70 day one-tangent to 25.9 for 65 day no-tangent. I’ve never really studied the phase angles for the various solutions and the trend is not obvious, and it seems like I’ve seen some angles out of that range. So I have to ask myself not only what the range is exactly, but if there is a way to make it work for the angles outside of the range.<br /><br />It sure doesn’t seem like it, but I’m going to do some investigating as time allows. It’s high time I modified the program to run repeatedly and write the results to a file for a spreadsheet.<br /><br />But pending the discovery of something cool and totally unexpected from that investigation, I have to say that the answer is:<br /><br />A: For the case where you burn your rockets to leave, then coast, then burn your rockets to arrive, you have choices only within a range of phase angles, <b>for most of the time the angular relationship between Earth and Mars is such that there is no possible flight path.</b> Making significant burns mid-flight would probably increase the choices and perhaps the range of angles, but would always require more energy for the same time of flight.<br /><br />Note that I left the door open for ion engines. These flight paths are not at all simple, but they are still similar to an ellipse. Everything I’ve read so far on ion engines is about spiraling paths to get there over much longer periods <div class="Discussion_UserSignature"> </div>

 

[scottb50]

Given enough time even a Smart-1 profile could get you to Mars, it might take a number of years though. It actually worked a lot better than predicted with Smart-1, it arrived ahead of schedule.<br /> The impracticality of enroute boosting, and impossibility of continuous boosting for decreasing the transit time also plays into the equation. Even looking at ion engines enroute creates a problem, I doubt they would add that much DeltaV in such a relatively short time, and if they did it would take a proportionally larger amount of propellant to get rid of the aded momentum entering Mars orbit. The possibility of providing the minimal escaqpe velocity and building up Delta V enroute with ion engines might make more sense, less propellant to leave orbit and the same to enter Mars orbit. Whether that would be a good trade-off is the catch, the added mass of ion engines leaving Earth orbit may be more than the propellant to simply apply the needed energy all at once and coast enroute.<br /> <div class="Discussion_UserSignature"> </div>

 

[mental_avenger]

Sorry I haven't responded lately. Two weeks ago my computer crashed, big time. I have spent a lot of time trying to get it running again, but have been hitting nothing but roadblocks. In the meantime I have been using my secondary system, an older HP, but it also has some problems and is a little slow. Anyhow, all my data was on the main system, and as near as I can tell, I accidentally erased most of it, along with the backup. I lost thousands of documents and thousands of photos, including the last 1500 photos I took with my digital camera.. Most of the missing stuff can be rebuilt, in time, but I am pretty upset about the irreplacable 1500 photos. Anyhow, that's my problem.<br /><br />In the meantime, I'd like to commend Dan Casale on his excellent summary of the Colinization Thread. It is very helpful to see all that data in one place. Good job.<br /><br />kadetken,<br />That is an excellent list of references, certainly more than I have. I can see how you would have a definite Lunar Leaning. Do you think your opinions would be different if you had as much information on Mars?<br /><br />I am rather tied up with work right now, but I'll stop in once in a while.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[halman]

Spacester,<br /><br />For some reason, I have never had difficulty accepting that there are only certain 'windows' for trips to Mars using our level of technology. I envisioned the Earth and Mars moving in circles around the Sun, with the Earth moving faster than Mars. Knowing that the only path from Earth to Mars is a curve, which is created by the Sun's gravity, and that the amount of energy used to leave Earth's orbit determined how shallow the curve could be, as well as the fact that there are only certain times when any of the curves connect the position of both Earth and Mars, it seemed straightforward.<br /><br />With unlimeted energy AND unlimited reaction mass, it would be possible to pick a very short, shallow curve to reach the destination, which my favorite science fiction writers incorporated into their stories all the time. But I kept seeing those two little dots going in circles, and they don't move at the same speed, so sometimes one is on the other side of the Sun from the other, and sometimes they are next to each other. I learned at a fairly early age that our ability to change the speed of a ship traveling between those dots is very small, and gets smaller the more mass that is incorporated into the ship.<br /><br />I have never wanted to travel to Mars, for some reason, so I never felt that there should be a way, somehow, if we could only find it. Space is pretty big, and getting around out there is always going to take a while. Just getting to the Moon seemed like a long trip to me. (Imagine spending 10 days sitting in the front seat of the car. No way!) <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[halman]

Mental_Avenger,<br /><br />You have my deepest condolances. I am a photographer also, and I know that there is no way to replace the pictures that matter the most. I have come to the realization that there may be some merit in the Redundant Array of Independent Disk method of data storage. Not having the funds to buy several hard drives, I have settled on trying to always use two on any computer, with the data that I treasure on a disk that is seperate from the one that the operating system is on.<br /><br />Out of stupidity and and greed, I tried to increase the clock rate on my main computer. It was working alright before I started messing with it, but the motherboard manual said that it should be able to do more. Now, it won't do anything. Oh, well. I am still able to use a computer, I just have to settle for one that is only 1/2 as fast as the one that I used to have. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[najab]

<blockquote><font class="small">In reply to:</font><hr /><p>Q: Is it possible to leave any time you want, and by using whatever time of flight and whatever energy you need to make it work, rendezvous with Mars?<p><hr /></p></p></blockquote>A: If either travel time or energy is unlimited, yes. As either gets increasingly finite the solutions decrease. For practical purposes, the available energy is finite and fixed and so only a limited number of solutions exist - each with varying travel times.

 

[mental_avenger]

Spacester,<br />Those figures look correct, for an eliptical orbit that intersects Mar's orbit at a tangent. That is the closest we can come to matching orbits with Mars as we come up on it from behind. It would require the least braking to achive Mars orbit.<br /><br />But what about a path that slingshots past the Sun? I don't have a way to model this, but it seems like there must be a path that takes a “shortcut” past the Sun at such an angle that it would end up in an orbit that is tangent to Mar's orbit. That should present at least one window opposite of a Hohmann window. I understand that the distance traveled would actually be further that way, but the portion of the orbit that loops around the Sun would be a lot faster than a Hohmann Transfer orbit.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[halman]

Mental_Avenger,<br /><br />You asked about a transfer orbit to Mars which 'slingshots past the Sun'. To acheive this, you must de-accelerate substanially, to lose most of the Earth's orbital velocity, which is about 18 miles per second. You will regain all of that velocity as you fall into the Sun's gravity well. Depending on how the orbit is perturbed by the Sun, you will rise up the far side of the well, to the vicinity of the Earth's orbit. An additional velocity change while closest to the Sun, one which increases the velocity, will throw you further out to the orbit of Mars. However, your trajectory will be at a tangent to the Martian orbit, so another velocity change will be needed to enter orbit around Mars. This could be accomplished with aerobraking, or an additional engine burn.<br /><br />Depending on how close your orbit comes to the Sun, travel time to Mars can be reduced to a couple of weeks. However, the penalty is in the amount of energy required to complete the mission. The shorter the transit time, the more energy needed. I don't know the exact figures, but for every pound of payload, you are looking at several times the delta V required for a Hohmann transfer orbit. A Saturn 5 could probably put 100 pounds in Martian orbit in about 10 days. However, that 100 pounds will be exposed to surface temperatures high enough to melt titanium, as the orbit will pass within a couple of million miles of the Sun.<br /> <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[mental_avenger]

Several points. There is no need to go that close to the Sun. <br /><br />The resultant orbital path, after it passes the Sun, should be determined by the initial path and velocity. It should be possible to achive an eliptical orbit that has one apogee at Mars orbit, and the other well inside Earth orbit. The object would be to achieve an orbit where the apogee is tangent to the orbit of Mars at a time when Mars was there. <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>

 

[halman]

Mental_Avenger,<br /><br />You are correct that traveling so close to the Sun is unnecessary. I was illustrating an extreme example of what is a practically infinte array of possible orbits to Mars.<br /><br />Most of these orbits require large changes of velocity, which is not possible with the rocket technology currently available.<br /><br />Until much more advanced propulsion systems are available, we are limited by our technology to very long transit times and very rare launch windows when sending mass to Mars. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[dan_casale]

I think we have gotten stuck on this issue and really should move on. Because except for the living payloads it is all about payload to the surface. So no matter what size the rocket, we will be looking for how much we can load into it. Only in the event of critical failure will we be considering how fast something can arrive to the surface.<br /><br />So where does that leave us?<br />What will be the economy of our Moon/Mars base? How will we repay Earth for the launch and equipment costs?

 

[spacester]

Just a note on the alternate path of going close to the sun . . .<br /><br />There is no such thing as a slingshot maneuver as proposed. You are already in a heliocentric orbit. You can change your orbit, but the "occupied node" is still the Sun. It's the same frame of reference, the same gravity well.<br /><br />A "slingshot" at a planet works by changing the <b>direction</b> of the velocity vector. You enter and leave the planet's gravity well at the same <b>magnitude</b> of velocity relative to the sun. This is the trick, you cannot do this trick while staying in the same gravity well.<br /><br />Going close to the Sun does not "deflect" the path. The path was already controlled by the Sun - the same ellipse before and after. All that happens is that you get hot.<br /><br />In any case, there is no shortcut. To go from Earth to a point nearer the Sun, you are committing to a low periapse (nearest approach to the Sun). At the same time, you want your apoapse to be at least the radius of Mars' orbit. This means that you will be travelling more than half of the orbit of the ellipse - from Earth to periapse and then from periapse to apoapse. Compare this with any other transfer path, which is always half of an orbit (Hohmann) or less.<br /><br />Also, going close to the Sun would require a much larger deltaV than any conventional transfer path, where your orbital energy is somewhere between that of an Earth orbit and a Mars Orbit.<br /><br />Whan I read about the Messenger mission and how hard it is to get to Mercury I scoffed. Until I did the math. In general terms, accessing the inner solar system is actually harder than going to Mars.<br /><br />This is really hard to explain without pictures. Trust me, there is no shortcut, either in terms of time or energy.<br /><br />Orbital Mechanics is a harsh mistress. <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> </div>

 

[spacester]

<font color="yellow">What will be the economy of our Moon/Mars base?</font><br /><br />People paying for the priviege of BEING THERE so that they can DO THINGS. Science, exploration, recreation, it's all good. <div class="Discussion_UserSignature"> </div>

 

[dan_casale]

I think I asked the wrong question. Additionally that question is premature. So lets backup again....<br />How many colonists will be launched with each launch window? <br />For what ever reason, lets assume 1 Moon/Mars launch window every two years and equipment launch windows every year.<br /><br />Please assign jobs to the colonists.<br /><br />What equipment will be launched and when?<br /><br />

 

[dan_casale]

To help stimulate the discussion I will also put forth my own opinion.<br /><br />Each group of colonists should consist of the following personel. Each group will become a seperate community within easy commute of each other, until there are at least 10 seperate communities.<br /><br />Colonists: 60 (30/30 - male/female under 35)<br />2 - doctors/vets<br />2 - medical assistants<br />10 - farmer/rancher<br />3 - engineer/fabricators<br />3 - blacksmiths<br />3 - computer programmers/network engineers<br />2 - ecologists<br />20 - miners/geologists<br />5 - cooks<br />10 - mechanics<br /><br />Equipment launched before colonists:<br />Mining equipment:<br />Trucks<br />Bulldozers<br />Crane<br />Smelter<br />Forge<br />Weilding equipment<br />Tunnel Boring Machine<br />Habitat Human/animal<br />Solar panels<br />Electralisis machine - for spliting water.<br />Spectral analizer<br />Spare parts<br /><br />Mining Goals:<br />Oxygen<br />Hydrogen<br />Water<br />Carbon<br />Nitrogen<br />Silicon<br />Aluminum<br />Helium-3/Helium<br />Platinum group metals<br />Iron<br /><br />Habitat goals:<br />50-80 deg F.<br />1 Bar atmosphere with Earth like composition.<br />100 sq ft personal space per colonist<br />1000 sq ft open space per colonist<br />CELSS type recycling system after 3 years<br />Room for 10,000 colonists within 20 years<br /><br />Economic goals:<br />Trade with Earth/Moon/Mars<br />Self sufficient within 20 years<br /><br />Population goals:<br />Year/#/comments <br />1 - 120 - 2 launches from Earth<br />3 - 180 - 2 launches from Earth, 1 group returns<br />5 - 420 - 5 launches from Earth, 2 groups return<br />7 - 600 - 5 launches from Earth, 2 groups return<br />9 - 1080 - 10 launches from Earth, 2 groups return<br />11 - 1560 - same<br />13 - 2140<br />15 - 2720<br />17 - 3300<br />19 - 3880

 

[eldensmith]

Dan, did you forget the nuclear reactors? Or did I miss it on your list?

 

[spayss]

10 mechanics? Try a couple hundred for that much equipment. and you need huge maintenance shops (employing several hundred) And where are the hundred of machinists to manufacture new parts? What happens when the bolts break on a bulldozer tread and the replacement parts don't fit? I've worked around bulldozers and they have a thousand parts that can break at any moment. And speaking of cranes... <br /><br /> So naive a list.

 

[dan_casale]

ELdenSmith:<br />If you look at the colonization document in an earlier post you will see that several types of nuclear power are discussed. But for a small colony, nuclear power might be too labor intensive when compared to Solar PV. PV has a complex manufacturing process but I believe it is less complex than mining/refining uranium.<br /><br />Spayss:<br />I think your estimate of "a couple hundred" mechanics is a bit more than most cities of 300,000 people have. Yes maintenance shops that will hold the equipment will need to be built. Hopefully from native (Moon/Mars) materials. The blacksmiths will have to take the place of "the hundreds of machinists to manufacture new parts". It will be slow work but if they can't make it, it will need to be ordered from Earth and may require a 2 year lead time. If the bulldozers break down, the colonists will have to dig and haul by hand. Not very profitable.<br /><br /> "So naive a list."<br />It was not intended to be complete, just a starting point. Thanks for your contribution.

 

[spayss]

"If the bulldozers break down"<br /><br /> What? you mean 'when' they break down and how many times in a week under conditions that are novel and unique. Where are these 'blacksmiths' going to work? Their tools? forges? What happens when (not if) their tools break...switches fail...wires need replacing...what wire? oops wrong switch..<br /><br /> Do you have any idea of how much infrastructure one industrial 'machine' needs on Earth? Send out for a part..to where? Even on the ISS, orbiting in LEO, not pushing any earth or doing mechanical 'work', there's a supply of 'gadgets' sent up with each supply flight to take care of unforseen needs. On Mars Duct tape and a set of tools from Sears won't keep a bulldozer going....where are you going to overhaul the engine and rebuild the transmission? Straighten a bent frame? Who fixes (with what) the cherry picker that burns a motor when hoisting out the engine?<br /><br /> The technology infrastructure to maintain more than a couple humans on Mars will be mind boggling.

 

[eldensmith]

<i>If you look at the colonization document in an earlier post you will see that several types of nuclear power are discussed. But for a small colony, nuclear power might be too labor intensive when compared to Solar PV. PV has a complex manufacturing process but I believe it is less complex than mining/refining uranium. </i><br /><br />I am jumping in mid-stream, and apologize if I've missed some basics. But, why won't your Terran sponsors spring for some nice nuclear reactors? Paying to send 60+ people to Mars and not include reactors and pebble bed based fuel supplies just seems to be "roughing it" without necessity.

 

[dan_casale]

Yes, truely When is the correct word. The heavy machinery will be needed to start with, but it may not be necessary to exist as a viable colony. Yes the technology level of any colony will drop an 1800's level. But it will have to be expected and planed for. Which is why the colony must grow as fast as possible until it is able to sustain its own technology. It is a very difficult undertaking, but it isn't impossible.

 

[dan_casale]

The technology level of any new colony will drop until it reaches a level that can be supplied from Earth or built on-site. The more colonists that exist the easier the job becomes. It would take several thousand people to maintain a low tech 1800's colony. In the very hostile environment of Moon/Mars, 60 people would not be able to more than dig in and wait to die. Genetically speaking 10,000 people is the very edge of survival.

 

[spayss]

Dan, I agree. Anything beyond a couple astronauts living in a sealed tin can waiting for the next spacecraft to take them back to Earth will require a critical mass of humans. Otherwise it will never get beyond a 'mission' stage no different from Apollo.